boards: x86: qemu: initialize flash simulator before EEPROM emulator

On the x86 QEMU boards the EEPROM emulator uses the simulated flash as
backend.

Change the default initialization priority for the EEPROM drivers to ensure
the flash simulator is ready before initializing the EEPROM emulator.

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>